1. Field of the Invention
The present invention relates to a method for adjusting characteristics of a dielectric filter the characteristics of which change by adjusting the dimension, etc., of a fixed adjusting part of the dielectric filter.
2. Description of the Related Art
Up to now, in order to adjust characteristics of a dielectric filter in which fixed electrode films are formed in a dielectric block, when the adjustment is manually carried out by an operator, the adjustment is made by the method of trial and error, and after having gained the knowledge of adjustment an operator in charge is trained. This has resulted in both an increase in the time of adjustment and a lowering of the yield. Then, in order to cope with these problems, applications such as Japanese Unexamined Patent Application Publication No. 4-236505, Japanese Unexamined Patent Application Publication No. 4-236506, and Japanese Unexamined Patent Application Publication No. 6-45802 have been made.
In Japanese Unexamined Patent Application Publication No. 4-236505, based on the envelope of peaks in the reflection loss characteristic of a filter, an adjusting part is determined by theoretical reasoning; in Japanese Unexamined Patent Application Publication No. 4-236506, based on a figure obtained by connecting the peaks and valleys in a reflection loss characteristic, an evaluation function is sought; and in Japanese Unexamined Patent Application Publication No. 6-45802, the error between a reflection loss characteristic and the theoretical value is sought at sampling points of the frequency axis of the reflection loss characteristic which is equally divided, adjustments are carried out in stages, and the adjustment is finished when the evaluation function becomes smaller.
However, in the methods shown in Japanese Unexamined Patent Application Publication No. 4-236505, Japanese Unexamined Patent Application Publication No. 4-236506, and Japanese Unexamined Patent Application Publication No. 6-45802, it is not clearly understood whether or not the value of an adjusting device (for example, resonant frequency of a resonator in a certain stage) is out of its target value, and accordingly there is a problem that the adjustment cannot be necessarily accurately made.
It is an object of the present invention to provide a method for adjusting characteristics of a dielectric filter in which the experience and skill of adjustment and visual knowledge are not required in actual adjustments, an adjustment by the method of trial and error is reduced, and an automatic adjustment is surely made.
In the present invention, a method for adjusting characteristics of a dielectric filter comprises the steps of measuring characteristics of a dielectric filter provided with a plurality of stages of resonators; and seeking pole frequencies and a balance of heights of peaks in at least a reflection loss characteristic out of the characteristics and, based on the pole frequencies and the balance of height of peaks, determining an adjusting part and a degree of adjustment with reference to a database.
Furthermore, in the method for adjusting characteristics of a dielectric filter, the steps further comprises measuring the center frequency of passband of the dielectric filter, seeking the difference between the center frequency and its target frequency, and, based on the difference, determining an adjusting par and a degree of adjustment with reference to the database.
Thus, the relationship of pole frequencies and a balance of height of peaks in a reflection loss characteristic to an adjusting part and a degree of adjustment is constructed as a database in advance, and then the reflection loss characteristic of a practical dielectric filter for adjustment is measured and, based on the pole frequencies and the balance of heights of the peaks, the adjusting part and the degree of adjustment are surely determined with reference to the database.
The pole frequencies in the above reflection loss characteristic do not represent the frequencies of discrete resonators, but the frequencies in coupled modes when the resonators are coupled to each other, and accordingly the pole frequencies are intuitively and visually easy to understand and give theoretical clear indexes for adjustment. The above database is constructed in such a way that the data showing the relationship of pole frequencies and balances of height of peaks in reflection loss characteristics to various patterns of dispersion of adjusting devices (resonant devices and coupling devices as objects for adjustment when the adjusting devices are represented by their equivalent circuits) are obtained by making use of the knowledge of skilled workers for adjustment and theoretical analyses or by using a simulator and thus the database is constructed.
Furthermore, in addition to the above reflection loss characteristic, as the difference between the center frequency of passband and its target frequency is also connected with the difference between resonant frequencies of the resonant devices, taking also the center frequencies of passband into consideration makes an adjusting part and a degree of adjustment more surely determined.